Power tool having proportioning transmission

ABSTRACT

Fastener setting power tool having a proportioning transmission capable of repeatedly applying fastener setting torque within rigorous torque tolerance limits irrespective of the rate of fastener deceleration.

limited States atent hitehouse POWER TOOL HAVING PROPORTIONINGTRANSMISSION Inventor: Hugh L. Whitehouse, Lyndhurst, Ohio Assignee: The Stanley Works, New Britain, Conn.

Filed: May 13, 1970 Appl. No.: 36,951

US. Cl. ..l73/12, 64/27 CT, 73/139,

81/52.4, 173/163, 192/150 Int. Cl ..B25b 23/14 Field of Search 173/12,163; 64/27 CT;

mama lWm;;;7//////////// May 30, 1972 Primary Examiner-Emest R. PurserAttorneyPrutzman, Hayes, Kalb & Chilton [57] ABSTRACT Fastener settingpower tool having a proportioning transmission capable of repeatedlyapplying fastener setting torque within rigorous torque tolerance limitsirrespective of the rate of fastener deceleration.

24 Claims, 6 Drawing Figures EYIIIIIIIIAYII Patented May 30, 1972 2Sheets-Sheet l ATTORNEYS POWER TOOL HAVING PROPORTIONING TRANSMISSIONFIELD OF THE INVENTION This invention generally relates to the powerfastening art and particularly concerns a precision torque limitingdevice for an air tool.

BACKGROUND OF THE INVENTION The tightening of threaded fastenersfrequently requires that a torque load applied to a fastener be within apermissible tolerance range. Applied torque loading close to desiredfastener torque may be achieved by conventional power tools withoutsubstantial difficulty when the fastener resistance steadily increasesto gradually slow down the tool as the fastener is being tightened. Suchjobs are referred to as socalledsoftjobs.

Difficulties, however, are presented by hard" jobs in attaining closetorque tolerance requirements wherein fastener loading builds up soquickly as to result in almost instantaneous arrest of the fastener. Asthe output end of a conventional tool is brought to a hard slam stopfrom a high-speed freerunning condition, an inertial impact of highmagnitude is all too frequently transmitted from the driving parts ofthe tool to the fastener, resulting in a finally tightened fastenerhaving a torque loading well beyond a maximum torque tolerance limit.

The continuously expanding use of assembled components has resulted inan ever increasing number of applications requiring the utmost care insetting a wide variety of fasteners to stringent torque tolerancelimits. No single assembly tool is known which will precisely controlthe peak applied torque within close tolerance requirements for a widevariety of jobs including not only soft but also extremely hard" jobswherein, e.g., 30 fastener rotation may be specified between freerunning and desired full fastener torque.

Increased demand for precisely torqued jobs has also resulted inadditional need for reliable verification of the peak applied torqueloading of a fastener and, frequently, for a'continuous reading of theinstantaneous torque delivered to a job under running load conditions.

BRIEF SUMMARY OF THE INVENTION The present invention relates generallyto rotary power tools for setting fasteners and more particularly to arotary power tool having a new and improved torsional drive for applyingthe fastener setting torque.

A primary object of this invention is to provide an improved power toolcapable of applying precisely controlled torque to a fastenerirrespective of the deceleration rate of the fastener being tightened.

Another object of this invention is to provide an improved proportioningtransmission usable with a power tool having speed characteristics ininverse relation to its load characteristics and which minimizesinertial torque transfer to a fastener to closely match the fastenertorque applied to a predetermined torque desired, regardless of whetherthe fastener setting operation is a typical soft or hard type job.

Still another object of this invention is the provision of an improvedproportioning transmission of the type described having a compact ruggedconstruction which is quick and easy to manufacture and assemble.

A further object of this invention is to provide an improved power toolcapable of accurately and continuously indicating the torque beingapplied during a fastener setting operation as well as for measuring thepeak applied fastener torque. Included in this object is the aim ofproviding a tool having a suitable torque indicator which is readilycalibrated and quick and easy to use for verifying the torque load beingapplied to a fastener.

Other objects will be in part obvious and in part pointed out in moredetail hereinafter.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forth certainillustrative embodiments and are indicative of the various ways in whichthe principle of the invention is employed.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a side view, partly in section and partly broken away, showinga part of a power tool incorporating this invention;

FIG. 2 is a side view of the tool of FIG. 1, partly broken away, showinga portion of one embodiment of a torque indicator provided in accordancewith this invention;

FIG. 3 is a longitudinal side view, partly in section and partly brokenaway, showing a second embodiment of a torque indicator provided inaccordance with this invention;

FIG. 4 is a cross-sectional view, partly broken away, taken generallyalong line 4-4 of FIG. 3;

FIG. 5 is a schematic diagram of still another embodiment of a torqueindicator device provided in accordance with this invention; and

FIG. 6 is a graphical representation of torque transmitted to a fastenerby the power tool of this invention during a fastener setting operation.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring'in detail to the drawingsand particularly to that embodiment of the invention illustrated inFIGS. 1 and 2, a power tool 10 is shown having a motor such as theillustrated air motor 12 which will be understood to be connected to asuitable source of air pressure, not shown, for rotating vanes 14 of arotor 16. The rotor 16 is drivingly connected through conventionalgearing, not shown, within a gear housing 18 to a spindle 20 supportedfor rotation by suitable bearings such as at 22.

To apply a precisely controlled peak applied fastener torque which isclosely matched to a desired predetermined torque load for a widevariety of not only soft" but also hard" jobs within stringent tolerancelimits, the power tool 10 of this invention incorporates a proportioningtransmission 24 coupled between the spindle 20 and an output drive 26for minimizing any increase in torque beyond a desired full fastenerload.

More specifically, the proportioning transmission 24 includes a tubulardriving member 28 with an enlarged input end 30 having a splinedconnection to the spindle 20. The driving member 28 is shown having anextension 32 received in coaxial telescoped relation within acomplementary extension 34 of a tubular driven member 36 whichterminates in abutting relation to a shoulder 38 on the driving member28. The driven member 36 has an enlarged output end 40 with a spindle 41shown as being splined to effect a suitable driving connection to theoutput drive 26. The output drive 26 will be understood to be adaptedfor use with any one of a variety of conventional toolholders, notshown, for tightening different types of fasteners, typically threadedfasteners, onto a workpiece.

In the specific illustrated embodiment, the driving member extension 32projects into the driven member extension 34 a distance preferably morethan half its full length and the members 28, 36 are suitablydimensioned to provide mutual rotary bearing support while additionallyacting to maintain one another in coaxial alignment. A portion of thedriven member 36 is shown having a reduced internal diameter adjacentits output end 40, this internal diameter preferably being dimensionedequal to that of the driving member 28 to form a chamber 42 of agenerally continuous, uniform diameter extending between the input andoutput ends 30, 40 of the driving and driven members 28 and 36. Themaximum outer diameters of members 28 and 36 are shown to be generallyequal to one another but less than the internal diameter of aproportioning transmission housing 44 which circumferentially extends inspaced relation about the members 28, 36.

In accordance with this invention, the proportioning transmission 24features a kinetic energy absorption device which in the specifiedillustrated embodiment is shown as a helical torsion spring 46 coaxiallyreceived within the chamber 42. The spring 46 is formed with straightoffset arms 48, 50 at its opposite ends respectively captured inelongated openings 52, 54 extending longitudinally of the enlarged endsof the driving and driven members 28, 36. The spring 46 is wound suchthat angular deflection responsive to rotation of the spindle 20relative to the output drive 26 contracts the coils of the spring 46 andaxially lengthens the spring 46 to a proportionate extent. To provideefficient rotary power transmission while at the same time ensuring asubstantial energy absorption capacity, the spring 46 is shown havingits coils closely wound and positioned between the ends of the tubularmembers 28, 36 with freedom of movement for unrestricted axialdeflection and radial contraction upon being twisted under applicationof a load.

Upon energizing the air motor 12, its rotor 16 accelerates to afree-running no-load speed, and the drive between the tubular members28, 36 is almost immediately synchronized with the spring 46 remainingin a relatively relaxed state as shown in FIG. 1. As the fastenerresistance builds up, the drive torque output of the tool increases fromzero inversely to the loading of the motor by the spring 46. In a softjob, the tool 10 slows down gradually as fastener resistance totightening builds up slowly, and little inertial torque is transmittedto the fastener due to the relatively low, gradual rate of fastenerdeceleration. Accordingly, peak applied torque normally will be closelymatched to static motor torque at the time of shutoff or stall. However,precisely controlled application of torque becomes increasinglydifficult as fastener resistance builds up more quickly to suddenlyincrease the rate of deceleration of the output drive 26 of the tool 10.Under such conditions, the inertial torque of the rotating mass, whichis proportional to its angular deceleration, could possibly impose anexcessive torque impact loading on the fastener, driving it beyond anacceptable maximum torque tolerance limit.

By the provision of the proportioning transmission 24 of this inventionwherein its energy absorption spring 46 is loaded from a relativelyrelaxed condition at free-running no-load speed of the motor 12,inertial torque loading of the spring 46 commences simultaneously withthe drive torque loading upon starting of running load conditionswhereby the inertial torque transmitted to a fastener has been found tobe significantly reduced while the kinetic energy of the deceleratingtool parts is absorbed and/or dissipated by the spring 46 even underextremely stringent hardjob applications.

For example, the worst condition would occur if a fastener wereinstantaneously arrested from a free-running no-load speed. In thisregard, reference is made to the graph in FIG. 6 wherein the torqueapplied to a fastener is plotted against spring twist under a conditionwherein a fastener is instantaneously arrested. The graph is based,e.g., upon a motor, the speed characteristics of which are an inversefunction of its load characteristics, and the use of a proportioningtransmission spring 46 of a given constant linear rate sufircient todecelerate the motor 12 and its associated drive parts from afree-running no-load speed under such running load conditions. Theapplied spring torque shown in the graph is a function of its springrate, the drive torque/speed characteristics of the drive parts andtheir moment of inertia, it being understood that the relatively lowmass of the spring and its moment of inertia together with that of thedriven parts is disregarded for purposes of this explanation.

Assuming the output drive 26 instantaneously slams to a stop, the totaltorque applied by the spring 46 will be equal to the sum of the motordrive torque and the inertial torque of the decelerating drive parts.With the fastener being decelerated at its maximum possible rate, themotor drive torque initially increases nonlinearly from zero to thepoint where the rate of increase in the motor drive torque equals therate of increase in the spring torque, during which initial period therate of increase in inertial torque diminishes. Once the rate ofincrease in the motor drive torque equals the spring rate, i.e., thepoint B on the line A--A in FIG. 6, the rotating drive parts willthereafter decelerate at a constant rate whereby the inertial torquewill remain constant and the drive torque will increase linearly. Thiscondition of dynamic equilibrium continues until the motor 12 is eithershut off or stalled, whichever occurs first, depending on the type ofpower tool with which the proportioning transmission 24 of thisinvention is being used.

As the motor 12 is decelerating under such running load conditions, itskinetic energy is being absorbed by the proportioning transmissionspring 46 and only static forces will be transmitted to the fastener,thereby limiting the peak applied fastener torque to the sum of themaximum inertial torque and the maximum motor drive torque.

By virtue of the above-described proportioning transmission 24, anyso-called overshoot beyond a desired full fastener torque loading willbe closely limited to approximately the maximum inertial torquetransmitted to the fastener during a setting operation and, as thespring is progressively loaded throughout fastener running, the inertialtorque is minimized. Since the spring 46 is in an unloaded condition atfree-running no-load motor speed, the unstressed spring 46 twistscoincident with initial application of load whereby the maximum inertialtorque applied to the fastener may be limited, even under hard" jobapplications, to an absolute magnitude within accepted tolerancerequirements.

As an example, the air motor 12 may be assumed to be equipped with aproportioning transmission 24 of the type disclosed with a typicalspring rate of about 30 foot pounds per 360 twist of the spring 46. Ifthe motor 12 were set to stall or shut off at a desired full fastenerload of, say, 18 foot pounds torque, and assuming a 12:1 gear reductionfrom the rotor 16 to the spindle 20, the spring 46 upon arrest of itsoutput end would be capable of decelerating the motor 12 fromfreerunning to stall or shut off in about eight motor revolutions.During deceleration the spring 46 would absorb the kinetic energy of therotating mass at a rate of about 2.5 foot pounds per 30 spring twist(one motor revolution). If the output drive 26 were arrestedinstantaneously (again, the worst condition for controlling the inertialeffects of the decelerating driving parts), the drive torque of themotor 12 would initially increase nonlinearly from zero until its rateof increase equals that of the applied spring torque. The inertialtorque then becomes constant, and referring to FIG. 6 which graphicallyrepresents this example, such a condition would appear to occur between35 and 40 spring twist, or shortly after one motor revolution. Themaximum inertial torque applied to the fastener as indicated in FIG. 6is less than 2.5 foot pounds torque applied by the spring 46 in onemotor revolution. As the overshoot approximately equals the maximuminertial torque transmitted to the fastener, an overshoot of, say, even2 foot pounds beyond the desired 18 foot pounds full fastener loadamounts to only about 11 percent. In practice wherein at least somefastener advance, say, 30 or 40, is permitted between free-runningno-load speed of the output drive 26 to desired full fastener load, itwill be seen that the overshoot will likely be reduced to an evensmaller percentage of desired full fastener load and still be wellwithin acceptable tolerance requirements even for such hard" jobapplications.

Should the motor 12 rebound upon stopping, any tendency of loosening thetightened fastener is minimized by an automatic energy dissipatingaction of the spring 46 which, upon being unwound, prevents reversetorquing to an extent of the stored kinetic energy.

In accordance with another aspect of this invention, any need to auditeach individual job to verify that the finally tightened condition ofthe fastener is within permissible torque indicating device which isresponsive to the loading of the spring 46 and which may be readilyadapted to provide accurate indication of the applied fastener torque bysuitable measuring and/or signal means.

The embodiment shown in FIGS. 1 and 2 illustrates an indicating device56 which is suited not only to measure peak applied fastener torque ofeach job but also to provide a continuous monitor during fastenerrundown which reflects instantaneous applied fastener torque at anygiven time during a setting operation.

The spring loading as reflected by relative rotation of the driving anddriven members 28, 36 is used for indicating applied fastener torque asthe proportioning transmission spring 46 is being wound up. As theoutput drive 26 decelerates relative to the spindle 20, driving member28 winds up the spring 46 and simultaneously causes post 58 to trackwithin a helical guideway 60 of preselected pitch formed in drivingmember 28. The post 58 extends radially outwardly through an axiallyextending guide opening 62 in the driven member 36 and is secured to asleeve 64 supported for longitudinal sliding movement on the drivenmember 36 in the clearance between the driven member and the housing 44.Sleeve 64 maintains the post 58 in camming engagement with member 28within its guideway 60, while the rotating driving member 28 earns thepost 58 toward the output end of the tool and longitudinally displacesthe sleeve 64 along the outer surface of the driven member 36 a lineardistance proportional to the extent of the spring twist imposed duringfastener setting.

The above-described torque sensing means is used to longitudinallydisplace a suitable manually resettable pointer 66 for indicatingapplied fastener torque. As illustrated, the pointer 66 is received formovement in a longitudinally extending slot 68 in the transmissionhousing 44 and is actuated by longitudinal displacement of the sleeve64. The pointer 66 is preferably closely fitted to the housing 44 with alight frictional load such that upon moving from its illustrated zerotorque position toward the output end of the tool 10, the pointer 66will automatically remain in the extreme position to which it was movedduring fastener setting for showing peak applied torque as indicated byindicia 70 on the housing 44. If desired, the indicia may be calibratedin foot pounds torque to conveniently provide a direct readout of thepeak fastener torque applied. Once the spring 46 is permitted to unwind,the torque sensing sleeve 64 is automatically retracted to itsillustrated zero torque position and the pointer 66 then may be manuallyreset to condition the torque indicator 56 for the next operation. Ifdesired, markings may be provided on the housing 44 indicative ofminimum and maximum torque tolerance limits to enable an operator tomake a simple, accurate determination of whether a fastener has been setwithin preselected tolerance requirements.

Another torque indicator device is shown in FIGS. 3 and 4 having asleeve 64A which is mechanically moved as in the previously describedembodiment for sensing applied torque and actuating an indicator. Sleeve64A is shown carrying a movable contact 72 which bridges any one ofthree pairs of stationary contacts 74A, 74B and 74C shown embedded inlongitudinally spaced locations in a plastic insert 76 which is suitedto be snap fitted into the slot 68A in the housing 44A. Each set ofstationary contacts is shown connected by lead wires 78 to any suitablesignaling device 80 and the contacts are located relative to the path ofmovement of the bridging contact 72 such that a first contact pair 74Aindicates when the tool 10 has been put on a job; the second contactpair 748 will signal when a minimum torque tolerance limit has beenreached; and the third contact pair 74C will indicate when a maximumtorque tolerance limit has been exceeded.

The torque indicator schematically shown in FIG. 5 provides anarrangement suitable for use with the tool 10 to provide a directreadout of applied fastener torque. A bridging contact 82 similar tothat shown in FIG. 3 is mounted, e.g., on a sleeve, not shown, formovement along a conductor rail 84 to complete a circuit connection to avariable resistor 86 disposed longitudinally of the tool whereby theextent of relative rotary movement between the tubular members 28, 36 isreflected in a reading, e.g., from a meter 88 suitably calibrated toindicate fastener torque delivered to a job.

As will be readily apparent, the devices shown in FIGS. 35 could beadapted to produce audible signals or be used in connection with avariety of devices located, if desired, remotely from the tool 10 tooperate a permanent record card punch or other device suitable to meetthe requirements of a particular job. The disclosed monitoring featurealso may be employed for actuating a shutoff mechanism or disconnectingdriven and driving clutch elements of a clutch type tool, not shown, ata predetermined applied torque. For example, motive power of theillustrated tool 10 may be controlled by suitable mechanical linkage,not shown, actuated by the sleeve 64A or by a signaling device locatedin the path of travel of sleeve 64A as shown in FIG. 4, wherein it willbe understood that the contact pair 74C may be adjustably positionedalong the axial path of the sleeve 64A to terminate power application ofthe tool 10 at a selected torque level.

A power tool constructed in accordance with this invention is not onlyof compact, rugged construction, particularly suited to apply preciselylimited torque in a broad range of different fastener setting operationshaving rigorous torque requirements, but is also quick and easy tomanufacture, assemble and calibrate. In addition, the disclosed powertool is capable of providing a continuous readout of the torque as it isbeing applied to a job as well as providing an accurate measurement ofpeak applied fastener torque.

As will be apparent to persons skilled in the art, variousmodifications, adaptations and variations of the foregoing specificdisclosure can be made without departing from the teachings of thepresent invention.

I claim:

1. A power tool for setting fasteners to a specified torque comprising amotor having a rotary drive and adapted to be energized to rotate therotary drive at a specified free-running no-load speed and with a drivetorque which increases as the rotary drive speed decreases from saidno-load speed, a rotary output for setting fasteners, and unloadedtorsion spring means interconnecting the rotary drive and rotary outputfor driving the rotary output, the torsion spring means havingresistance to torsional deflection which increases with deflection andbeing operable to be angularly deflected continually and unrestrictivelyfrom its unloaded condition to provide for smooth deceleration of therotary drive by the rotary output from its free-running no-load speedwith the motor remaining energized.

2. The power tool of claim 1 wherein the motor is a rotary fluid motorset to stall or shut off at said specified torque, and wherein thespring means has a spring rate sufficient to decelerate the fluid motorto stall or shut off in approximately eight motor revolutions uponinstantaneous arrest of the rotary output from free-running no-loadspeed.

3. The power tool of claim 1 further including torque indicating meansoperable in response to loading of the spring means for indicatingapplied fastener torque.

4. The power tool of claim 1 wherein the spring means is a helicaltorsion coil spring having opposite ends drivingly connected to therotary drive and the rotary output and its coils positioned therebetweenwith freedom of movement for unrestricted axial deflection and radialcontraction responsive to loading.

5. The power tool of claim 1 wherein the spring means has a spring ratesufficient to decelerate the rotary drive when the rotary output isarrested without further angular movement from free-running no-loadspeed while limiting peak applied fastener torque during suchdeceleration to a magnitude less than percent of said specified torque.

6. The power tool of claim 1 further including selectively operativesignal means for indicating an acceptable torque range, and a torquesensing device controlling operation of the signal means responsive torelative rotation between the rotary drive and the rotary output.

7. The power tool of claim 1 wherein the torsion spring means is activeunder running load conditions and has a spring rate sufficient todecelerate the motor when the rotary output is instantaneously arrestedfrom free-running no-load speed while limiting peak applied fastenertorque during such deceleration to a magnitude less than 125 percent ofsaid specified torque.

8. The power tool of claim 1 further including a torque indicator forindicating peak applied fastener torque, and a torque sensing device foractuating the torque indicator, the torque sensing device being movableresponsive to relative relation between the rotary drive and the rotaryoutput.

9. The power tool of claim 8 wherein the torque indicator is operableunder running load conditions and provides a continuous monitor ofapplied fastener torque.

10. The power tool of claim 1 wherein the torsion spring means has aspring rate sufficient to decelerate the rotary drive throughout thefull range of running load conditions, and wherein the torsion springmeans is operable for applying a relatively constant peak appliedfastener torque irrespective of the deceleration rate of the rotaryoutput due to fastener resistance to torque loading.

11. The power tool of claim 10 wherein said peak applied fastener torqueexceeds said specified torque to an extent approximately equal to themaximum inertial torque transmitted from the rotary drive to the rotaryoutput, and wherein torsional deflection of the torsion spring means iscoincident with initial fastener torque loading for minimizing themagnitude of the transmitted inertial torque.

12. The power tool of claim 10 wherein the torsion spring means limitssaid peak applied fastener torque to a magnitude less than 125 percentof said specified torque.

13. A power tool useable in setting fasteners to a predetermined fullfastener load and comprising power operated rotary drive means, rotaryoutput means for setting fasteners, and a transmission including torsionspring means coupling the drive means to the output means, the torsionspring means being active under running load conditions and continuouslymaintaining a resilient driving connection between the drive means andthe output means under running load conditions irrespective of themagnitude of peak applied fastener torque, the transmission including ahelical cam member connected to one of the drive means and output means,a linearly movable cam follower in camming engagement with the helicalcam, member and a follower guide member supported on the other of thedrive means and output means, the helical cam and follower guide membersbeing relatively rotatable, and the cam follower being operative forsensing torque applied by the torsion spring means upon rotation of thedrive means relative to the output means as indicated by linear movementof the cam follower.

14. The power tool of claim 13 further including display means operatedby the cam follower for providing a visual indication of the torqueapplied by the spring means.

15. The power tool of claim 13 further including a transmission housing,the drive means and the output means being substantially aligned forrotation about a common axis, and fastener torque indicating meansincluding a resettable marker supported for movement on the housingresponsive to movement of the cam follower in one linear direction withrespect to the axis of rotation during loading of the spring means.

16. The power tool of claim 13 wherein the helical cam and followerguide members are tubular members in coaxial telescoped relation.

17. The power tool of claim 16 wherein the spring means is a helicaltorsion spring received within the tubular helical cam and followerguide members and having opposite ends coupled to the drive means andoutput means with freedom of movement within the guide members forunrestricted radial contraction and axial extension responsive toloading.

18. The power tool of claim 13 further including control means forcontrolling application of motive power to the output means of the tool,and actuating means for actuating the control means for terminating theapplication of motive power to the output means.

19. The power tool of claim 18 wherein the actuating means is located inand adjustable along the path of linear movement of the cam follower.

20. In a power tool of a type having power operated rotary drive means,rotary output means for setting fasteners, an elongated housing, and atransmission received within the housing and including spring meanscoupling the drive means and output means, a torque indicating mechanismcomprising a torque sensing device supported for linear movementlongitudinally of the housing, the linear movement of the torque sensingdevice being proportional to deflection of the spring means uponrelative rotation of the drive means and output means during a fastenersetting operation, and an indicator operable responsive to linearmovement of the torque sensing device for indicating torque applied bythe spring means.

21. The torque indicating mechanism of claim 20 wherein the drive meansand the output means are substantially aligned for rotation about acommon axis and respectively include tubular portions in coaxialtelescoped relation, and wherein the torque sensing device includes aslide drivingly connected to one of the tubular portions and supportedon the other thereof for linear movement within the housing uponrelative rotation of the drive means and output means.

22. The torque indicating mechanism of claim 21 wherein the indicator isreceived in a slot formed longitudinally of the housing in the path oflinear movement of the slide.

23, In a power tool of a type having power operated rotary drive means,rotary output means for setting fasteners, an elongated housing, and atransmission received within the housing and including spring meanscoupling the drive means and output means, a torque indicating mechanismcomprising a torque sensing device received for movement within thehousing in operative alignment with an opening formed in the housing,and mounting means mounting the torque sensing device for movement inproportion to loading of the spring means upon relative rotation of thedrive means and output means for providing an indication of the torqueapplied during a fastener setting operation.

24. The torque indicating device of claim 23 wherein the housing openingis provided by a slot extending longitudinally of the housing, whereinan indicator is received in the slot, and wherein the torque sensingdevice is supported by the mounting means for movement longitudinally ofthe housing, the torque sensing device being movable a linear distanceproportional to loading of the spring means.

1. A power tool for setting fasteners to a specified torque comprising amotor having a rotary drive and adapted to be energized to rotate therotary drive at a specified free-running no-load speed and with a drivetorque which increases as the rotary drive speed decreases from saidno-load speed, a rotary output for setting fasteners, and unloadedtorsion spring means interconnecting the rotary drive and rotary outputfor driving the rotary output, the torsion spring means havingresistance to torsional deflection which increases with deflection andbeing operable to be angularly deflectEd continually and unrestrictivelyfrom its unloaded condition to provide for smooth deceleration of therotary drive by the rotary output from its free-running no-load speedwith the motor remaining energized.
 2. The power tool of claim 1 whereinthe motor is a rotary fluid motor set to stall or shut off at saidspecified torque, and wherein the spring means has a spring ratesufficient to decelerate the fluid motor to stall or shut off inapproximately eight motor revolutions upon instantaneous arrest of therotary output from free-running no-load speed.
 3. The power tool ofclaim 1 further including torque indicating means operable in responseto loading of the spring means for indicating applied fastener torque.4. The power tool of claim 1 wherein the spring means is a helicaltorsion coil spring having opposite ends drivingly connected to therotary drive and the rotary output and its coils positioned therebetweenwith freedom of movement for unrestricted axial deflection and radialcontraction responsive to loading.
 5. The power tool of claim 1 whereinthe spring means has a spring rate sufficient to decelerate the rotarydrive when the rotary output is arrested without further angularmovement from free-running no-load speed while limiting peak appliedfastener torque during such deceleration to a magnitude less than 125percent of said specified torque.
 6. The power tool of claim 1 furtherincluding selectively operative signal means for indicating anacceptable torque range, and a torque sensing device controllingoperation of the signal means responsive to relative rotation betweenthe rotary drive and the rotary output.
 7. The power tool of claim 1wherein the torsion spring means is active under running load conditionsand has a spring rate sufficient to decelerate the motor when the rotaryoutput is instantaneously arrested from free-running no-load speed whilelimiting peak applied fastener torque during such deceleration to amagnitude less than 125 percent of said specified torque.
 8. The powertool of claim 1 further including a torque indicator for indicating peakapplied fastener torque, and a torque sensing device for actuating thetorque indicator, the torque sensing device being movable responsive torelative relation between the rotary drive and the rotary output.
 9. Thepower tool of claim 8 wherein the torque indicator is operable underrunning load conditions and provides a continuous monitor of appliedfastener torque.
 10. The power tool of claim 1 wherein the torsionspring means has a spring rate sufficient to decelerate the rotary drivethroughout the full range of running load conditions, and wherein thetorsion spring means is operable for applying a relatively constant peakapplied fastener torque irrespective of the deceleration rate of therotary output due to fastener resistance to torque loading.
 11. Thepower tool of claim 10 wherein said peak applied fastener torque exceedssaid specified torque to an extent approximately equal to the maximuminertial torque transmitted from the rotary drive to the rotary output,and wherein torsional deflection of the torsion spring means iscoincident with initial fastener torque loading for minimizing themagnitude of the transmitted inertial torque.
 12. The power tool ofclaim 10 wherein the torsion spring means limits said peak appliedfastener torque to a magnitude less than 125 percent of said specifiedtorque.
 13. A power tool useable in setting fasteners to a predeterminedfull fastener load and comprising power operated rotary drive means,rotary output means for setting fasteners, and a transmission includingtorsion spring means coupling the drive means to the output means, thetorsion spring means being active under running load conditions andcontinuously maintaining a resilient driving connection between thedrive means and the output means under running load conditionsirrespective of the magnitude of peak applieD fastener torque, thetransmission including a helical cam member connected to one of thedrive means and output means, a linearly movable cam follower in cammingengagement with the helical cam, member and a follower guide membersupported on the other of the drive means and output means, the helicalcam and follower guide members being relatively rotatable, and the camfollower being operative for sensing torque applied by the torsionspring means upon rotation of the drive means relative to the outputmeans as indicated by linear movement of the cam follower.
 14. The powertool of claim 13 further including display means operated by the camfollower for providing a visual indication of the torque applied by thespring means.
 15. The power tool of claim 13 further including atransmission housing, the drive means and the output means beingsubstantially aligned for rotation about a common axis, and fastenertorque indicating means including a resettable marker supported formovement on the housing responsive to movement of the cam follower inone linear direction with respect to the axis of rotation during loadingof the spring means.
 16. The power tool of claim 13 wherein the helicalcam and follower guide members are tubular members in coaxial telescopedrelation.
 17. The power tool of claim 16 wherein the spring means is ahelical torsion spring received within the tubular helical cam andfollower guide members and having opposite ends coupled to the drivemeans and output means with freedom of movement within the guide membersfor unrestricted radial contraction and axial extension responsive toloading.
 18. The power tool of claim 13 further including control meansfor controlling application of motive power to the output means of thetool, and actuating means for actuating the control means forterminating the application of motive power to the output means.
 19. Thepower tool of claim 18 wherein the actuating means is located in andadjustable along the path of linear movement of the cam follower.
 20. Ina power tool of a type having power operated rotary drive means, rotaryoutput means for setting fasteners, an elongated housing, and atransmission received within the housing and including spring meanscoupling the drive means and output means, a torque indicating mechanismcomprising a torque sensing device supported for linear movementlongitudinally of the housing, the linear movement of the torque sensingdevice being proportional to deflection of the spring means uponrelative rotation of the drive means and output means during a fastenersetting operation, and an indicator operable responsive to linearmovement of the torque sensing device for indicating torque applied bythe spring means.
 21. The torque indicating mechanism of claim 20wherein the drive means and the output means are substantially alignedfor rotation about a common axis and respectively include tubularportions in coaxial telescoped relation, and wherein the torque sensingdevice includes a slide drivingly connected to one of the tubularportions and supported on the other thereof for linear movement withinthe housing upon relative rotation of the drive means and output means.22. The torque indicating mechanism of claim 21 wherein the indicator isreceived in a slot formed longitudinally of the housing in the path oflinear movement of the slide.
 23. In a power tool of a type having poweroperated rotary drive means, rotary output means for setting fasteners,an elongated housing, and a transmission received within the housing andincluding spring means coupling the drive means and output means, atorque indicating mechanism comprising a torque sensing device receivedfor movement within the housing in operative alignment with an openingformed in the housing, and mounting means mounting the torque sensingdevice for movement in proportion to loading of the spring means uponrelative rotation of the drive means and output means for providing anindicAtion of the torque applied during a fastener setting operation.24. The torque indicating device of claim 23 wherein the housing openingis provided by a slot extending longitudinally of the housing, whereinan indicator is received in the slot, and wherein the torque sensingdevice is supported by the mounting means for movement longitudinally ofthe housing, the torque sensing device being movable a linear distanceproportional to loading of the spring means.